Golf ball

ABSTRACT

A golf ball for amateur golfers is endowed with both an excellent flight and a good feel at impact that is soft and solid when hit by the average golfer whose head speed is not very high. The golf ball, which includes a core and a cover, has a compressive deformation A when subjected to a final load of 5 kg from an initial load of 0.2 kg that is 0.21 mm or less, a compressive deformation B when subjected to a final load of 30 kg from an initial load of 5 kg that is from 0.72 to 0.90 mm and a compressive deformation C when subjected to a final load of 60 kg from an initial load of 5 kg that is from 1.55 to 1.80 mm.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2018-169572 filed in Japan on Sep. 11,2018, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a golf ball which has a core and acover, and is intended for use by amateur golfers lacking a fast headspeed.

BACKGROUND ART

In the field of golf balls for amateur golfers, numerous balls intendedto satisfy amateur players in terms of flight performance and feel havehitherto been developed. For example, JP-A H08-280845 describes a golfball wherein, using the amount of compressive deformation when a finalload of 5 kg is applied from an initial load state of 0.2 kg as anindicator of the influence exerted on the ball properties when a smallimpact force has acted upon a golf ball, this value is set in the rangeof from 0.26 to 0.40 mm. However, this golf ball is a spin-type ballthat is targeted primarily at the spin on approach shots, and does notfully satisfy the flight performance desired on shots with a driver.

In addition, a variety of functional, multi-piece solid golf balls inwhich the ball has a multilayer construction and the surface hardnessesof the respective layers—i.e., the core, envelope layer, intermediatelayer and cover (outermost layer)—are optimized have been described.These include the multi-piece solid golf balls disclosed in JP-A2014-132955, JP-A 2015-173860, JP-A 2016-16117 and JP-A 2016-179052. Thegolf balls disclosed in these patent publications satisfy the followinghardness relationship: ball surface hardness>intermediate layer surfacehardness>envelope layer surface hardness<core surface hardness, andimpart an excellent flight performance even when used by amateur golferslacking a fast head speed. However, these prior-art golf balls do notoptimize the amount of compressive deformation when subjected to a finalload of 5 kg from an initial load state of 0.2 kg and the amount ofcompressive deformation when subjected to a final load of 30 kg from aninitial load state of 5 kg. That is, no attention has been paid to howthe golf ball properties are affected by the magnitude of the impactforce acting on the ball, and so there remains room for improvement inobtaining a good flight performance and a good feel at impact in golfball products for amateur golfers.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golfball for amateur golfers which has an excellent flight when hit by theaverage golfer whose head speed is not that high and which also has agood feel at impact that is both soft and solid.

As a result of extensive investigations, we have focused on therelationship, in golf balls having a core and a cover, between themagnitude of the force of impact applied to the golf ball and the ballcharacteristics of flight performance and feel. We have discovered inparticular that, in the amount of compressive deformation by the golfball, by specifying the following respective compressive deformations:the compressive deformation A when the ball is subjected to a final loadof 5 kg from an initial load state of 0.2 kg, the compressivedeformation B when the ball is subjected to a final load of 30 kg froman initial load state of 5 kg, the compressive deformation C when theball is subjected to a final load of 60 kg from an initial load state of5 kg and the compressive deformation D when the ball is subjected to afinal load of 130 kg from an initial load state of 10 kg, as well as theratios therebetween, a flight performance that is satisfactory when theball is hit with all golf clubs, including drivers (W #1) and irons, canbe fully obtained by golfers lacking a fast head speed, in addition towhich a feel that is both soft and solid can be obtained.

Accordingly, in a first aspect, the invention provides a golf ball thatincludes a core and a cover, wherein the ball has an amount ofcompressive deformation such that the compressive deformation A when theball is subjected to a final load of 5 kg from an initial load state of0.2 kg is 0.21 mm or less, the compressive deformation B when the ballis subjected to a final load of 30 kg from an initial load state of 5 kgis from 0.72 to 0.90 mm, and the compressive deformation C when the ballis subjected to a final load of 60 kg from an initial load state of 5 kgis from 1.55 to 1.80 mm.

In a preferred embodiment of the golf ball of the invention, thecompressive deformation D when the ball is subjected to a final load of130 kg from an initial load state of 10 kg is from 2.80 to 3.40 mm.

In another preferred embodiment of the inventive golf ball, the ratioD/C between compressive deformation D and compressive deformation C isfrom 1.80 to 1.90.

In yet another preferred embodiment, the ratio D/B between compressivedeformation D and compressive deformation B is from 3.65 to 4.20.

In still another preferred embodiment, the ratio D/A between compressivedeformation D and compressive deformation A is from 16.0 to 25.0.

In a further preferred embodiment, the ball additionally includes,between the core and the cover, at least an envelope layer and anintermediate layer, thus having a construction of four or more layersthat includes a core, an envelope layer, an intermediate layer and acover.

In a still further preferred embodiment, the golf ball satisfies thefollowing surface hardness relationship:

(1) Shore D hardness at surface of cover>Shore D hardness at surface ofintermediate layer>Shore D hardness at surface of envelope layer>Shore Dhardness at center of core.

In another preferred embodiment of the inventive golf ball, letting Ccbe the Shore C hardness at a center of the core and Cs be the Shore Chardness at a surface of the core, the Shore C hardness differencebetween the surface and center of the core (Cs−Cc) is 20 or more.

In yet another preferred embodiment, the cover has a paint film layerformed on a surface thereof, which paint film layer has a materialhardness that is higher than the core center hardness (Cc).

In still another preferred embodiment, the golf ball satisfies thefollowing initial velocity relationships (2), (3) and (4):

(2) −0.8 m/s≤(ball initial velocity−core initial velocity)≤0 m/s,(3) −0.4 m/s≤(ball initial velocity−initial velocity of intermediatelayer-encased sphere)≤0.4 m/s, and(4) 0 m/s≤(initial velocity of intermediate layer−encased sphere−initialvelocity of envelope layer-encased sphere)≤0.4 m/s.

In a second aspect, the invention provides a golf ball that includes acore and a cover, wherein the ball has an amount of compressivedeformation such that, letting A be the compressive deformation when theball is subjected to a final load of 5 kg from an initial load state of0.2 kg, B be the compressive deformation when the ball is subjected to afinal load of 30 kg from an initial load state of 5 kg, C be thecompressive deformation when the ball is subjected to a final load of 60kg from an initial load state of 5 kg and D be the compressivedeformation when the ball is subjected to a final load of 130 kg from aninitial load state of 10 kg, D has a value of from 2.80 to 3.40 mm, theratio D/C is from 1.80 to 1.90, the ratio D/B is from 3.65 to 4.20 andthe ratio D/A is from 16.0 to 25.0.

Advantageous Effects of the Invention

The golf ball of the invention has an excellent flight performance whenhit by golfers whose head speeds are not that high and also has a goodfeel at impact that is both soft and solid, making it highly suitablefor use by amateur golfers.

BRIEF DESCRIPTION OF THE DIAGRAMS

The FIGURE is a schematic cross-sectional view of a golf ball having afour-layer construction according to one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects, features and advantages of the invention will become moreapparent from the following detailed description taken in conjunctionwith the appended diagrams.

The golf ball of the invention has a core and a cover. In thisinvention, the cover refers to the member positioned as the outermostlayer in the ball construction and typically is formed by injectionmolding or the like. Numerous dimples are typically formed on the outersurface of the cover at the same time that the cover material isinjection molded.

The core has a diameter of preferably at least 34.0 mm, more preferablyat least 34.5 mm, and even more preferably at least 35.0 mm. The upperlimit is preferably not more than 37.0 mm, more preferably not more than36.5 mm, and even more preferably not more than 36.0 mm. When the corediameter is too small, the spin rate on shots with a driver (W #1) maybecome high, as a result of which it may not be possible to achieve thedesired distance. On the other hand, when the core diameter is toolarge, the durability to repeated impact may worsen or the feel atimpact may worsen.

The core has an amount of compressive deformation (mm) when subjected toa final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf)which, although not particularly limited, is preferably at least 3.0 mm,more preferably at least 3.5 mm, and even more preferably at least 4.0mm. The upper limit is preferably not more than 7.0 mm, more preferablynot more than 6.0 mm, and even more preferably not more than 5.0 mm.When the compressive deformation of the core is too small, i.e., whenthe core is too hard, the spin rate of the ball may rise excessively anda good distance may not be achieved, or the feel at impact may be toohard. On the other hand, when the compressive deformation of the core istoo large, i.e., when the core is too soft, the ball rebound may becometoo low and a good distance may not be achieved, the feel at impact maybe too soft, or the durability to cracking on repeated impact mayworsen.

The core is formed of a single layer or a plurality of layers of rubbermaterial. A rubber composition can be prepared as this core-formingrubber material by using a base rubber as the chief component andincluding, together with this, other ingredients such as aco-crosslinking agent, an organic peroxide, an inert filler and anorganosulfur compound. It is preferable to use polybutadiene as the baserubber.

Commercial products may be used as the polybutadiene. Illustrativeexamples include BR01, BR51 and BR730 (all products of JSR Corporation).The proportion of polybutadiene within the base rubber is preferably atleast 60 wt %, and more preferably at least 80 wt %. Rubber ingredientsother than the above polybutadienes may be included in the base rubber,provided that doing so does not detract from the advantageous effects ofthe invention. Examples of rubber ingredients other than the abovepolybutadienes include other polybutadienes and also other dienerubbers, such as styrene-butadiene rubbers, natural rubbers, isoprenerubbers and ethylene-propylene-diene rubbers.

Examples of co-crosslinking agents include unsaturated carboxylic acidsand metal salts of unsaturated carboxylic acids. Specific examples ofunsaturated carboxylic acids include acrylic acid, methacrylic acid,maleic acid and fumaric acid. The use of acrylic acid or methacrylicacid is especially preferred. Metal salts of unsaturated carboxylicacids are exemplified by, without particular limitation, the aboveunsaturated carboxylic acids that have been neutralized with desiredmetal ions. Specific examples include the zinc salts and magnesium saltsof methacrylic acid and acrylic acid. The use of zinc acrylate isespecially preferred.

The unsaturated carboxylic acid and/or metal salt thereof is included inan amount, per 100 parts by weight of the base rubber, which istypically at least 5 parts by weight, preferably at least 9 parts byweight, and more preferably at least 13 parts by weight. The amountincluded is typically not more than 60 parts by weight, preferably notmore than 50 parts by weight, and more preferably not more than 40 partsby weight. Too much may make the core too hard, giving the ball anunpleasant feel at impact, whereas too little may lower the rebound.

Commercial products may be used as the organic peroxide. Examples ofsuch products that may be suitably used include Percumyl D, Perhexa C-40and Perhexa 3M (all from NOF Corporation), and Luperco 231XL (fromAtoChem Co.). One of these may be used alone, or two or more may be usedtogether. The amount of organic peroxide included per 100 parts byweight of the base rubber is preferably at least 0.1 part by weight,more preferably at least 0.3 part by weight, even more preferably atleast 0.5 part by weight, and most preferably at least 0.6 part byweight. The upper limit is preferably not more than 5 parts by weight,more preferably not more than 4 parts by weight, even more preferablynot more than 3 parts by weight, and most preferably not more than 2.5parts by weight. When too much or too little is included, it may not bepossible to obtain a ball having a good feel, durability and rebound.

Another compounding ingredient typically included with the base rubberis an inert filler, preferred examples of which include zinc oxide,barium sulfate and calcium carbonate. One of these may be used alone, ortwo or more may be used together. The amount of inert filler includedper 100 parts by weight of the base rubber is preferably at least 1 partby weight, and more preferably at least 5 parts by weight. The upperlimit is preferably not more than 50 parts by weight, more preferablynot more than 40 parts by weight, and even more preferably not more than35 parts by weight. Too much or too little inert filler may make itimpossible to obtain a proper weight and a suitable rebound.

In addition, an antioxidant may be optionally included. Illustrativeexamples of suitable commercial antioxidants include Nocrac NS-6 andNocrac NS-30 (both available from Ouchi Shinko Chemical Industry Co.,Ltd.), and Yoshinox 425 (available from Yoshitomi PharmaceuticalIndustries, Ltd.). One of these may be used alone, or two or more may beused together.

The amount of antioxidant included per 100 parts by weight of the baserubber is set to 0 part by weight or more, preferably at least 0.05 partby weight, and more preferably at least 0.1 part by weight. The upperlimit is set to preferably not more than 3 parts by weight, morepreferably not more than 2 parts by weight, even more preferably notmore than 1 part by weight, and most preferably not more than 0.5 partby weight. Too much or too little antioxidant may make it impossible toachieve a suitable ball rebound and durability.

An organosulfur compound may be included in the core in order to imparta good resilience. The organosulfur compound is not particularlylimited, provided it can enhance the rebound of the golf ball. Exemplaryorganosulfur compounds include thiophenols, thionaphthols, halogenatedthiophenols, and metal salts of these. Specific examples includepentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol,p-chlorothiophenol, the zinc salt of pentachlorothiophenol, the zincsalt of pentafluorothiophenol, the zinc salt of pentabromothiophenol,the zinc salt of p-chlorothiophenol, and any of the following having 2to 4 sulfur atoms: diphenylpolysulfides, dibenzylpolysulfides,dibenzoylpolysulfides, dibenzothiazoylpolysulfides anddithiobenzoylpolysulfides. The use of the zinc salt ofpentachlorothiophenol is especially preferred.

The amount of organosulfur compound included per 100 parts by weight ofthe base rubber is 0 part by weight or more, and it is recommended thatthe amount be preferably at least 0.1 part by weight, and even morepreferably at least 0.2 part by weight, and that the upper limit bepreferably not more than 5 parts by weight, more preferably not morethan 3 parts by weight, and even more preferably not more than 2 partsby weight. Including too much organosulfur compound may make a greaterrebound-improving effect (particularly on shots with a W #1) unlikely tobe obtained, may make the core too soft or may worsen the feel of theball at impact. On the other hand, including too little may make arebound-improving effect unlikely.

Decomposition of the organic peroxide within the core formulation can bepromoted by the direct addition of water (or a water-containingmaterial) to the core material. The decomposition efficiency of theorganic peroxide within the core-forming rubber composition is known tochange with temperature; starting at a given temperature, thedecomposition efficiency rises with increasing temperature. If thetemperature is too high, the amount of decomposed radicals risesexcessively, leading to recombination between radicals and, ultimately,deactivation. As a result, fewer radicals act effectively incrosslinking. Here, when a heat of decomposition is generated bydecomposition of the organic peroxide at the time of core vulcanization,the vicinity of the core surface remains at substantially the sametemperature as the temperature of the vulcanization mold, but thetemperature near the core center, due to the build-up of heat ofdecomposition by the organic peroxide which has decomposed from theoutside, becomes considerably higher than the mold temperature. In caseswhere water (or a water-containing material) is added directly to thecore, because the water acts to promote decomposition of the organicperoxide, radical reactions like those described above can be made todiffer at the core center and core surface. That is, decomposition ofthe organic peroxide is further promoted near the center of the core,bringing about greater radical deactivation, which leads to a furtherdecrease in the amount of active radicals. As a result, it is possibleto obtain a core in which the crosslink densities at the core center andthe core surface differ markedly. It is also possible to obtain a corehaving different dynamic viscoelastic properties at the core center.

The water included in the core material is not particularly limited, andmay be distilled water or tap water. The use of distilled water that isfree of impurities is especially preferred. The amount of water includedper 100 parts by weight of the base rubber is preferably at least 0.1part by weight, and more preferably at least 0.3 part by weight. Theupper limit is preferably not more than 5 parts by weight, and morepreferably not more than 4 parts by weight.

The core can be produced by vulcanizing and curing the rubbercomposition containing the above ingredients. For example, the core canbe produced by using a Banbury mixer, roll mill or other mixingapparatus to intensively mix the rubber composition, subsequentlycompression molding or injection molding the mixture in a core mold, andcuring the resulting molded body by suitably heating it under conditionssufficient to allow the organic peroxide or co-crosslinking agent toact, such as at a temperature of between 100 and 200° C., preferablybetween 140 and 180° C., for 10 to 40 minutes.

The core may consist of a single layer alone, or may be formed as atwo-layer core consisting of an inner core layer and an outer corelayer. When the core is formed as a two-layer core consisting of aninner core layer and an outer core layer, the inner core layer and outercore layer materials may each be composed primarily of theabove-described rubber material. Also, the rubber material making up theouter core layer encasing the inner core layer may be the same as ordifferent from the inner core layer material. The details here are thesame as those given above for the ingredients of the core-forming rubbermaterial.

Next, the core hardness profile is described.

The core center has a hardness (Cc) which, expressed on the Shore Chardness scale, is preferably at least 50, more preferably at least 53,and even more preferably at least 55. The upper limit is preferably notmore than 65, more preferably not more than 62, and even more preferablynot more than 60. When this value is too large, the feel at impact maybecome hard, or the spin rate on full shots may rise, as a result ofwhich the intended distance may not be achieved. On the other hand, whenthis value is too small, the rebound may become low, resulting in a poordistance, or the durability to cracking on repeated impact may worsen.The Shore C hardness is the hardness value measured with a Shore Cdurometer in general accordance with ASTM D2240. Although, for example,the timing of the read-off of measurements differs from that in thetechnique used for measuring JIS-C hardness, the measured Shore Chardness values do not differ much from and, in fact, are closelysimilar to the JIS-C values.

Alternatively, the core center hardness (Cc) expressed on the Shore Dhardness scale is preferably at least 26, more preferably at least 28,and even more preferably at least 30. The upper limit is preferably notmore than 40, more preferably not more than 37, and even more preferablynot more than 34.

The core surface has a hardness (Cs) which, expressed on the Shore Chardness scale, is preferably at least 73, more preferably at least 77,and even more preferably at least 80. The upper limit is preferably notmore than 89, more preferably not more than 87, and even more preferablynot more than 85. A value outside of this range may lead to undesirableresults similar to those described above for the core center hardness(Cc).

Alternatively, the core surface hardness (Cs) expressed on the Shore Dhardness scale is preferably at least 40, more preferably at least 43,and even more preferably at least 45. The upper limit is preferably notmore than 54, more preferably not more than 52, and even more preferablynot more than 50.

The difference between the core surface hardness (Cs) and the corecenter hardness (Cc), expressed on the Shore C hardness scale, ispreferably at least 20, more preferably at least 22, and even morepreferably at least 24. The upper limit is preferably not more than 32,and more preferably not more than 30. When this value is too small, theball spin rate-lowering effect on shots with a driver may be inadequate,resulting in a poor distance. When this value is too large, the initialvelocity of the ball when struck may decrease, resulting in a poordistance, or the durability to cracking on repeated impact may worsen.

Next, the cover is described.

The cover has a material hardness on the Shore D scale which, althoughnot particularly limited, is preferably at least 55, more preferably atleast 59, and even more preferably at least 61. The upper limit ispreferably not more than 70, more preferably not more than 68, and evenmore preferably not more than 65. The surface hardness of the cover(also referred to herein as the “ball surface hardness”), expressed onthe Shore D scale, is preferably at least 61, more preferably at least65, and even more preferably at least 67. The upper limit is preferablynot more than 76, more preferably not more than 74, and even morepreferably not more than 71. When the material hardness of the cover andthe ball surface hardness are too much lower than the above respectiveranges, the spin rate of the ball on shots with a driver (W #1) may riseand the ball initial velocity may decrease, as a result of which a gooddistance may not be obtained. On the other hand, when the materialhardness of the cover and the ball surface hardness are too high, thedurability to cracking on repeated impact may worsen.

The cover has a thickness of preferably at least 0.6 mm, more preferablyat least 0.8 mm, and even more preferably at least 1.1 mm. The upperlimit in the cover thickness is preferably not more than 1.5 mm, morepreferably not more than 1.4 mm, and even more preferably not more than1.3 mm. When the cover is too thin, the durability to cracking onrepeated impact may worsen. When the cover is too thick, the spin rateof the ball on shots with a driver (W #1) may rise excessively and agood distance may not be obtained, or the feel at impact in the shortgame and on shots with a putter may be too hard.

Various types of thermoplastic resins, particularly ionomer resins, thatare employed as cover stock in golf balls may be suitably used as thecover material. Commercial products may be used as the ionomer resin.Alternatively, the cover-forming resin material that is used may be oneobtained by blending, of commercially available ionomer resins, ahigh-acid ionomer resin having an acid content of at least 18 wt % intoa conventional ionomer resin. The high rebound and the spinrate-lowering effect obtained with such a blend make it possible toachieve a good distance on shots with a driver (W #1). The amount ofsuch a high-acid ionomer resin included per 100 parts by weight of theresin material is preferably at least 10 wt %, more preferably at least30 wt %, and even more preferably at least 60 wt %. The upper limit isgenerally up to 100 wt %, preferably up to 90 wt %, and more preferablyup to 80 wt %. When the content of this high-acid ionomer resin is toolow, the spin rate on shots with a driver (W #1) may rise, resulting ina poor distance. On the other hand, when the content of the high-acidionomer resin is too high, the durability to cracking on repeated impactmay worsen.

The envelope layer and intermediate layer described below may beprovided between the core and cover. Suitable ball constructions in thepresent invention are not limited to two-piece golf balls having a coreand a single-layer cover; three-piece golf balls and four-piece golfballs may also be used. The use of golf balls composed of four layers—acore, an envelope layer, an intermediate layer and a cover—is especiallysuitable. Such golf balls are exemplified by the golf ball G shown inthe FIGURE. The golf ball G in the FIGURE has a core 1, an envelopelayer 2 encasing the core 1, an intermediate layer 3 encasing theenvelope layer 2, and a cover 4 encasing the intermediate layer 3. Thiscover 4 is positioned as the outermost layer, aside from a paint filmlayer, in the layer structure of the golf ball. The intermediate layerand the envelope layer may each be either a single layer or may beformed of two or more layers. Numerous dimples D are generally formed onthe surface of the cover (outermost layer) 4 in order to enhance theaerodynamic properties. In addition, a paint film layer 5 is formed onthe surface of the cover 4.

Next, the envelope layer is described.

The envelope layer has a material hardness on the Shore D scale which,although not particularly limited, is preferably at least 20, morepreferably at least 23, and even more preferably at least 27. The upperlimit is preferably not more than 45, more preferably not more than 42,and even more preferably not more than 40. The surface hardness of thesphere obtained by encasing the core with the envelope layer (envelopelayer-encased sphere), expressed on the Shore D scale, is preferably atleast 28, more preferably at least 31, and even more preferably at least35. The upper limit is preferably not more than 53, more preferably notmore than 50, and even more preferably not more than 48. When thematerial and surface hardnesses of the envelope layer are lower than theabove respective ranges, the spin rate of the ball on full shots mayrise excessively, resulting in a poor distance, or the durability of theball to repeated impact may worsen. On the other hand, when the materialand surface hardnesses are too high, the durability to cracking onrepeated impact may worsen or the spin rate on full shots may rise, as aresult of which, particularly on low head speed shots, a good distancemay not be achieved, and the feel at impact may worsen.

The envelope layer has a thickness of preferably at least 0.7 mm, morepreferably at least 0.9 mm, and even more preferably at least 1.1 mm.The upper limit in the envelope layer thickness is preferably not morethan 1.5 mm, more preferably not more than 1.4 mm, and even morepreferably not more than 1.3 mm. When this envelope layer is too thin,the durability to cracking on repeated impact may worsen or the feel atimpact may worsen. When the envelope layer is too thick, the spin rateof the ball on full shots may rise and a good distance may not beachieved.

The envelope layer material is not particularly limited, althoughvarious types of thermoplastic resin materials may be suitably employedfor this purpose. For example, use can be made of ionomer resins,urethane, amide, ester, olefin or styrene-type thermoplastic elastomers,and mixtures thereof. From the standpoint of obtaining a good rebound inthe desired hardness range, the use of a thermoplastic polyether esterelastomer is especially suitable.

The sphere obtained by encasing the core with the envelope layer(envelope layer-encased sphere) has an amount of compressive deformation(mm) when subjected to a final load of 1,275 N (130 kgf) from an initialload of 98 N (10 kgf) which, although not particularly limited, ispreferably at least 3.4 mm, more preferably at least 3.8 mm, and evenmore preferably at least 3.9 mm. The upper limit is preferably not morethan 4.7 mm, more preferably not more than 4.5 mm, and even morepreferably not more than 4.3 mm. When the compressive deformation of thesphere is too small, that is, when the sphere is too hard, the ball spinrate may rise excessively, resulting in a poor distance, or the feel atimpact may become too hard. On the other hand, when the compressivedeformation of the sphere is too large, that is, when the sphere is toosoft, the ball rebound may become too low, resulting in a poor distance,the feel at impact may become too soft, or the durability to cracking onrepeated impact may worsen.

Next, the intermediate layer is described.

The intermediate layer has a material hardness on the Shore D scalewhich, although not particularly limited, is preferably at least 40,more preferably at least 45, and even more preferably at least 50. Theupper limit is preferably not more than 62, more preferably not morethan 60, and even more preferably not more than 58. The surface hardnessof the sphere obtained by encasing the envelope layer-encased spherewith the intermediate layer (intermediate layer-encased sphere),expressed on the Shore D scale, is preferably at least 46, morepreferably at least 51, and even more preferably at least 56. The upperlimit is preferably not more than 68, more preferably not more than 66,and even more preferably not more than 64. When the material and surfacehardnesses of the intermediate layer are lower than the above respectiveranges, the spin rate of the ball on full shots may rise excessively,resulting in a poor distance, or the ball may cease to have a solid feelat impact. On the other hand, when the material and surface hardnessesare too high, the durability to cracking on repeated impact may worsenor the ball may cease to have a soft feel at impact.

The intermediate layer has a thickness of preferably at least 0.7 mm,more preferably at least 0.9 mm, and even more preferably at least 1.1mm. The upper limit in the intermediate layer thickness is preferablynot more than 1.5 mm, more preferably not more than 1.4 mm, and evenmore preferably not more than 1.35 mm. When the intermediate layer istoo thin, the durability to cracking on repeated impact may worsen orthe feel at impact may worsen. When the intermediate layer is too thick,the spin rate of the ball on full shots may rise and a good distance maynot be obtained.

The intermediate layer-forming material is not particularly limited andmay be a known resin. Examples of preferred materials include resincompositions containing as the essential ingredients:

100 parts by weight of a resin component composed of, in admixture,

(A) a base resin of (a-1) an olefin-unsaturated carboxylic acid randomcopolymer and/or a metal ion neutralization product of anolefin-unsaturated carboxylic acid random copolymer mixed with (a-2) anolefin-unsaturated carboxylic acid-unsaturated carboxylic acid esterrandom terpolymer and/or a metal ion neutralization product of anolefin-unsaturated carboxylic acid-unsaturated carboxylic acid esterrandom terpolymer in a weight ratio between 100:0 and 0:100, and

(B) a non-ionomeric thermoplastic elastomer in a weight ratio between100:0 and 50:50;

(C) from 5 to 80 parts by weight of a fatty acid and/or fatty acidderivative having a molecular weight of from 228 to 1,500; and

(D) from 0.1 to 17 parts by weight of a basic inorganic metal compoundcapable of neutralizing un-neutralized acid groups in components A andC.

Components A to D in the intermediate layer-forming resin materialdescribed in, for example, JP-A 2010-253268 may be advantageously usedas above components A to D.

A non-ionomeric thermoplastic elastomer may be included in theintermediate layer material. The amount of non-ionomeric thermoplasticelastomer included is preferably from 0 to 50 parts by weight per 100parts by weight of the total amount of the base resin.

Exemplary non-ionomeric thermoplastic elastomers include polyolefinelastomers (including polyolefin and metallocene polyolefins),polystyrene elastomers, diene polymers, polyacrylate polymers, polyamideelastomers, polyurethane elastomers, polyester elastomers andpolyacetals.

Depending on the intended use, optional additives may be suitablyincluded in the intermediate layer material. For example, pigments,dispersants, antioxidants, ultraviolet absorbers and light stabilizersmay be added. When these additives are included, the amount added per100 parts by weight of the overall base resin is preferably at least 0.1part by weight, and more preferably at least 0.5 part by weight. Theupper limit is preferably not more than 10 parts by weight, and morepreferably not more than 4 parts by weight.

The sphere obtained by encasing the envelope-encased sphere with theintermediate layer (intermediate layer-encased sphere) has an amount ofcompressive deformation when subjected to a final load of 1,275 N (130kgf) from an initial load of 98 N (10 kgf) which, although notparticularly limited, is preferably at least 3.3 mm, more preferably atleast 3.45 mm, and even more preferably at least 3.6 mm. The upper limitis preferably not more than 4.2 mm, more preferably not more than 4.0mm, and even more preferably not more than 3.8 mm. When the compressivedeformation of the sphere is too small, that is, when the sphere is toohard, the ball spin rate may rise excessively, resulting in a poordistance, or the feel at impact may become too hard. On the other hand,when the compressive deformation of the sphere is too large, that is,when the sphere is too soft, the ball rebound may become too low,resulting in a poor distance, the feel at impact may become too soft, orthe durability to cracking on repeated impact may worsen.

The manufacture of multi-piece solid golf balls in which theabove-described core, envelope layer, intermediate layer and cover(outermost layer) are formed as successive layers may be carried out bya customary method such as a known injection molding process. Forexample, a multi-piece golf ball can be obtained by successivelyinjection-molding the envelope layer material and the intermediate layermaterial over the core so as to obtain an intermediate layer-encasedsphere, and then injection-molding the cover material over theintermediate layer-encased sphere. Alternatively, the encasing layersmay each be formed by enclosing the sphere to be encased within twohalf-cups that have been pre-molded into hemispherical shapes and thenmolding under applied heat and pressure.

The compressive deformation A of the inventive golf ball when subjectedto a final load of 5 kg from an initial load state of 0.2 kg is 0.21 mmor less, preferably 0.19 mm or less, and more preferably 0.17 mm orless. The lower limit is preferably at least 0.10 mm, and morepreferably at least 0.12 mm. When this value becomes smaller, in caseswhere this is attributable to the cover hardness, the cover may be toohard and the durability of the ball to cracking under repeated impactmay worsen. Alternatively, when this value becomes smaller owing tocompression of an inner layer, the feel of the ball on full shots maybecome too hard. On the other hand, when the above value becomes larger,in cases where this is attributable to the cover hardness, the spin rateof the ball on full shots may end up rising, so that a good distance isnot achieved. Alternatively, when this value becomes larger owing tocompression of an inner layer, the ball may cease to have a crisp feelon full shots and a good distance may not be achieved.

The compressive deformation B of the inventive golf ball when subjectedto a final load of 30 kg from an initial load state of 5 kg ispreferably at least 0.72 mm, more preferably at least 0.73 mm, and evenmore preferably at least 0.74 mm. The upper limit is preferably not morethan 0.90 mm, more preferably not more than 0.88 mm, and even morepreferably not more than 0.86 mm. If this value is small, the ball mayhave too hard a feel when struck with a utility club (also abbreviatedbelow as “UT”) or an iron. On the other hand, if this value is large,the crisp feel of the ball when struck with a utility club or an ironmay diminish and a good distance may not be achieved.

The compressive deformation C of the inventive golf ball when subjectedto a final load of 60 kg from an initial load state of 5 kg ispreferably at least 1.55 mm, more preferably at least 1.56 mm, and evenmore preferably at least 1.58 mm. The upper limit is preferably not morethan 1.80 mm, more preferably not more than 1.77 mm, and even morepreferably not more than 1.74 mm. If this value is small, the ball mayhave too hard a feel at impact when struck with a utility club or aniron. On the other hand, if this value is large, the crisp feel of theball when struck with a utility club or an iron may diminish and a gooddistance may not be achieved.

The compressive deformation D of the inventive golf ball when subjectedto a final load of 130 kg from an initial load state of 10 kg ispreferably at least 2.80 mm, more preferably at least 2.90 mm, and evenmore preferably at least 2.95 mm. The upper limit is preferably not morethan 3.40 mm, more preferably not more than 3.30 mm, and even morepreferably not more than 3.15 mm. If this value is small, the spin rateof the ball may rise, resulting in a poor distance, or the feel of theball may become too hard. On the other hand, if this value is large, theball rebound may become too low, resulting in a poor distance, the feelof the ball may become too soft, or the durability to cracking underrepeated impact may worsen.

The ratio D/C between compressive deformation D and compressivedeformation C is preferably from 1.80 to 1.90. Outside of this range,the solid feel of the ball may worsen and impact conditions under whichthe distance falls may arise.

The ratio D/B between compressive deformation D and compressivedeformation B is preferably at least 3.65, more preferably at least3.67, and even more preferably at least 3.69. The upper limit ispreferably not more than 4.20, more preferably not more than 4.15, andeven more preferably not more than 4.10. Outside of this range, thesolid feel of the ball may worsen and impact conditions under which thedistance falls may arise.

The ratio D/A between compressive deformation D and compressivedeformation A is preferably at least 16.0, more preferably at least17.0, and even more preferably at least 17.5. The upper limit ispreferably not more than 25.0, more preferably not more than 24.0, andeven more preferably not more than 23.0. Outside of this range, the ballmay become too receptive to spin or the initial velocity of the ballwhen struck may decrease and, depending on the number of the golf club,the distance may decrease.

Surface Hardness Relationships Among Layers

In this invention, it is desirable for the hardness relationships amongthe layers to satisfy formula (1) below:

(1) Shore D hardness at cover surface>Shore D hardness at intermediatelayer surface>Shore D hardness at envelope layer surface>Shore Dhardness at core center.

Here, the hardness at the cover surface refers to the surface hardnessof the ball. The hardness at the intermediate layer surface refers tothe surface hardness of the intermediate layer-encased sphere, and thehardness at the envelope layer surface refers to the surface hardness ofthe envelope layer-encased sphere.

When the above hardness relationship is not satisfied, a good flightperformance and a feel at impact that is both soft and solid may not beobtained.

As indicated in the above formula, the cover surface hardness is largerthan the intermediate layer surface hardness. The differencetherebetween, i.e., the “cover surface hardness−intermediate layersurface hardness” value, expressed on the Shore D hardness scale, ispreferably from 1 to 14, more preferably from 3 to 10, and even morepreferably from 5 to 8. When this value is small, the spin rate of theball on full shots may end up rising, as a result of which a gooddistance may not be achieved. On the other hand, when this value islarge, the feel at impact may worsen or the durability to cracking onrepeated impact may worsen.

As indicated in the above formula, the intermediate layer surfacehardness is larger than the envelope layer surface hardness. Thedifference therebetween, i.e., the “intermediate layer surfacehardness−envelope layer surface hardness” value, expressed on the ShoreD hardness scale, is preferably from 10 to 28, more preferably from 13to 26, and even more preferably from 15 to 24. When this value is small,the spin rate of the ball on full shots may end up rising, as a resultof which a good distance may not be achieved. On the other hand, whenthis value is large, the feel at impact may worsen or the durability tocracking on repeated impact may worsen.

As indicated in the above formula, the envelope layer surface hardnessis larger than the core center hardness. The difference therebetween,i.e., the “envelope layer surface hardness−core center hardness” value,expressed on the Shore D hardness scale, is preferably from 3 to 23,more preferably from 5 to 20, and even more preferably from 7 to 17.Also, the “envelope layer surface hardness−core surface hardness” value,expressed on the Shore D hardness scale, is preferably from −20 to 8,more preferably from −15 to 5, and even more preferably from −10 to 2.When these values are small, the spin rate of the ball on full shots mayend up rising, as a result of which a good distance may not be achieved.On the other hand, when these values are large, the feel at impact mayworsen or the durability to cracking on repeated impact may worsen.

Also, the “core surface hardness−ball surface hardness” value, expressedon the Shore D hardness scale, is preferably from −30 to −10, morepreferably from −27 to −14, and even more preferably from −24 to −17.When this value is small, the solid feel of the ball at impact may belost or the durability to cracking on repeated impact may worsen. On theother hand, when this value is large, impact conditions may emerge underwhich the spin rate of the ball rises and a good distance is notachieved.

Compressive Deformation Relationships among Encased Spheres

Letting P and Q be the respective compressive deformations (mm) of thecore and the envelope layer-encased sphere when subjected to a finalload of 1,275 N (130 kg) from an initial load of 98 N (10 kgf), thevalue P−Q is preferably from 0 to 0.6 mm, more preferably from 0.1 to0.5 mm, and even more preferably from 0.2 to 0.4 mm. When this value issmall, the feel at impact may worsen or the durability to cracking underrepeated impact may worsen. When this value is large, the spin rate ofthe ball on full shots may end up rising, as a result of which a gooddistance may not be obtained.

Letting Q and R be the respective compressive deformations (mm) of theenvelope layer-encased sphere and the intermediate layer-encased spherewhen subjected to a final load of 1,275 N (130 kg) from an initial loadof 98 N (10 kgf), the value Q−R is preferably from 0.1 to 0.8 mm, morepreferably from 0.2 to 0.7 mm, and even more preferably from 0.3 to 0.6mm. When this value is small, the spin rate of the ball on full shotsmay end up rising, as a result of which a good distance may not beachieved. On the other hand, when this value is large, the feel atimpact may worsen or the durability to cracking on repeated impact mayworsen.

Letting P and D be the respective compressive deformations (mm) of thecore and the ball when subjected to a final load of 1,275 N (130 kg)from an initial load of 98 N (10 kgf), the value P−D is preferably from1.0 to 1.7 mm, more preferably from 1.1 to 1.6 mm, and even morepreferably from 1.2 to 1.5 mm. When this value is small, the spin rateof the ball on full shots may end up rising, as a result of which a gooddistance may not be achieved. On the other hand, when this value islarge, the solid feel at impact may be lost or the durability tocracking on repeated impact may worsen.

Initial Velocity Relationships Among Encased Spheres

The “ball initial velocity−core initial velocity” value is preferablyfrom −0.8 to 0 m/s, more preferably from −0.6 to −0.1 m/s, and even morepreferably from −0.5 to −0.3 m/s. When this value is too small, therebound of the overall ball may become low or the spin rate on fullshots may rise excessively, as a result of which a good distance may notbe obtained. On the other hand, when this value is too large, the covermay become hard and the durability to cracking on repeated impact mayworsen. As used herein, “initial velocity” refers to the initialvelocity of the various spheres—i.e., the ball, the core, and thesubsequently described intermediate layer-encased sphere and envelopelayer-encased sphere—as measured by the method, set forth in the Rulesof Golf, for measuring the initial velocity of golf balls using aninitial velocity measuring apparatus of the same type as the USGA drumrotation-type initial velocity instrument.

The “ball initial velocity−intermediate layer-encased sphere initialvelocity” value is preferably from −0.4 to 0.4 m/s, more preferably from−0.3 to 0.3 m/s, and even more preferably from −0.2 to 0.1 m/s. Whenthis value is too large, the spin rate-lowering effect on full shots maybe inadequate and a good distance may not be achieved, or the cover maybecome hard, worsening the durability to cracking on repeated impact. Onthe other hand, when this value is too small, the cover may become soft,as a result of which the spin rate on full shots may rise, resulting ina poor distance, or a solid feel at impact may not be obtained.

The “intermediate layer-encased sphere initial velocity−envelopelayer-encased sphere initial velocity” value is at least 0.0 m/s,preferably from 0.1 to 0.4 m/s, and more preferably from 0.15 to 0.3m/s. When this value is too small, the spin rate-lowering effect on fullshots may be inadequate and a good distance may not be achieved. On theother hand, when this value is too large, the intermediate layermaterial may become brittle and the durability to cracking on repeatedimpact may worsen.

Numerous dimples may be formed on the outside surface of the coverserving as the outermost layer. The number of dimples arranged on thecover surface, although not particularly limited, is preferably at least250, more preferably at least 300, and even more preferably at least320. The upper limit is preferably not more than 380, more preferablynot more than 350, and even more preferably not more than 340. When thenumber of dimples is higher than this range, the ball trajectory maybecome lower, as a result of which the distance traveled by the ball maydecrease. On the other hand, when the number of dimples is lower thatthis range, the ball trajectory may become higher, as a result of whicha good distance may not be achieved.

The dimple shapes used may be of one type or may be a combination of twoor more types suitably selected from among, for example, circularshapes, various polygonal shapes, dewdrop shapes and oval shapes. Whencircular dimples are used, the dimple diameter may be set to at leastabout 2.5 mm and up to about 6.5 mm, and the dimple depth may be set toat least 0.08 mm and up to 0.30 mm.

In order for the aerodynamic properties to be fully manifested, it isdesirable for the dimple coverage ratio on the spherical surface of thegolf ball, i.e., the dimple surface coverage SR, which is the sum of theindividual dimple surface areas, each defined by the flat planecircumscribed by the edge of a dimple, as a percentage of the sphericalsurface area of the ball were the ball to have no dimples thereon, to beset to at least 70% and not more than 90%. Also, to optimize the balltrajectory, it is desirable for the value V₀, defined as the spatialvolume of the individual dimples below the flat plane circumscribed bythe dimple edge, divided by the volume of the cylinder whose base is theflat plane and whose height is the maximum depth of the dimple from thebase, to be set to at least 0.35 and not more than 0.80. Moreover, it ispreferable for the ratio VR of the sum of the volumes of the individualdimples, each formed below the flat plane circumscribed by the edge of adimple, with respect to the volume of the ball sphere were the ballsurface to have no dimples thereon, to be set to at least 0.6% and notmore than 1.0%. Outside of the above ranges in these respective values,the resulting trajectory may not enable a good distance to be obtainedand so the ball may fail to travel a fully satisfactory distance.

To ensure a good ball appearance, it is preferable to apply a clearcoating onto the cover surface. The coating composition used in clearcoating is preferably one which uses two types of polyester polyol asthe base resin and uses a polyisocyanate as the curing agent. In thiscase, various organic solvents can be admixed depending on the intendedcoating conditions. Examples of organic solvents that can be usedinclude aromatic solvents such as toluene, xylene and ethylbenzene;ester solvents such as ethyl acetate, butyl acetate, propylene glycolmethyl ether acetate and propylene glycol methyl ether propionate;ketone solvents such as acetone, methyl ethyl ketone, methyl isobutylketone and cyclohexanone; ether solvents such as diethylene glycoldimethyl ether, diethylene glycol diethyl ether and dipropylene glycoldimethyl ether; alicyclic hydrocarbon solvents such as cyclohexane,methyl cyclohexane and ethyl cyclohexane; and petroleumhydrocarbon-based solvents such as mineral spirits.

The paint film layer (coating layer) obtained by clear coating has ahardness which, on the Shore C hardness scale, is preferably from 40 to80, more preferably from 47 to 72, and even more preferably from 55 to65. When the coating layer is too soft, mud may tend to stick to thesurface of the ball when used for golfing. On the other hand, when thecoating layer is too hard, it may tend to peel off when the ball isstruck.

The “core center hardness (Cc)−coating layer hardness” value on theShore C hardness scale is preferably from −15 to 5, more preferably from−10 to 0, and even more preferably from −7 to −5. When this value fallsoutside of the above range, the spin rate of the ball on full shots mayend up rising, as a result of which a good distance may not be achieved.

The paint film layer (coating layer) has a thickness of typically from 9to 22 μm, preferably from 11 to 20 μm, and more preferably from 13 to 18μm.

The multi-piece solid golf ball of the invention can be made to conformto the Rules of Golf for play. The inventive ball may be formed to adiameter which is such that the ball does not pass through a ring havingan inner diameter of 42.672 mm and is not more than 42.80 mm, and to aweight which is preferably between 45.0 and 45.93 g.

EXAMPLES

The following Examples and Comparative Examples are provided toillustrate the invention, and are not intended to limit the scopethereof.

Examples 1 to 4, Comparative Examples 1 to 5 Formation of Core

Solid cores were produced by preparing rubber compositions for therespective Examples and Comparative Examples shown in Table 1, and thenmolding/vulcanizing the compositions under vulcanization conditions of155° C. and 15 minutes.

TABLE 1 Core formulation Example Comparative Example (pbw) 1 2 3 4 1 2 34 5 Polybutadiene A 80 80 80 80 80 80 80 80 100 Polybutadiene B 20 20 2020 20 20 20 20 Zinc acrylate 28.2 26.9 29.6 28.2 28.2 29.6 30.9 29.627.0 Organic peroxide (1) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.6 Organicperoxide (2) 0.6 Water 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Antioxidant 0.10.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Barium sulfate 27.4 27.9 26.8 27.4 27.426.8 26.3 26.8 24.3 Zinc oxide 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 Zincsalt of pentachlorothiophenol 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Details onthe ingredients mentioned in Table 1 are given below. Polybutadiene A:Available under the trade name “BR 01” from JSR CorporationPolybutadiene B: Available under the trade name “BR 51” from JSRCorporation Zinc acrylate: Available as “ZN-DA85S” from Nippon ShokubaiCo., Ltd. Organic Peroxide (1): Dicumyl peroxide, available under thetrade name “Percumyl D” from NOF Corporation Organic Peroxide (2): Amixture of 1,1-di(t-butylperoxy)cyclohexane and silica, available underthe trade name “Perhexa C-40” from NOF Corporation Water: Pure water(from Seiki Chemical Industrial Co., Ltd.) Antioxidant:2,2′-Methylenebis(4-methyl-6-butylphenol), available under the tradename “Nocrac NS-6” from Ouchi Shinko Chemical Industry Co., Ltd. Bariumsulfate: Baryte powder available as “Barico #100” from Hakusui Tech Zincoxide: Available as “Zinc Oxide Grade 3” from Sakai Chemical Co., Ltd.Zinc salt of pentachlorothiophenol: Available from Wako Pure ChemicalIndustries, Ltd.

Formation of Envelope Layer and Intermediate Layer

Next, in each Example and Comparative Example other than ComparativeExample 5, an envelope layer was formed by injection molding theenvelope layer material formulated as shown in Table 2 over the core,following which the intermediate layer was formed by injection moldingthe intermediate layer material formulated as shown in the same table,thereby giving a sphere encased by an envelope layer and an intermediatelayer. In Comparative Example 5, an intermediate layer was formed byinjection molding the intermediate layer material formulated as shown inTable 2 over the core, thereby giving an intermediate layer-encasedsphere.

Formation of Cover (Outermost Layer)

Next, in all of the Examples and Comparative Examples, a cover(outermost layer) was formed by injection molding the cover materialformulated as shown in Table 2 over the intermediate layer-encasedsphere obtained as described above. A plurality of given dimples commonto all the Examples and Comparative Examples were formed at this time onthe surface of the cover.

TABLE 2 Resin composition (pbw) No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No.7 No. 8 Hytrel 4001 100 Hytrel 3001 100 HPF 2000 100 HPF 1000 100 56Himilan 1605 44 50 AM 7318 75 AM 7327 25 AM 7329 50 Surlyn 9320 70 AN4221C 30 Magnesium 60 stearate Magnesium 1.12 oxide Titanium oxide 4 4Trade names of the chief materials mentioned in the table are givenbelow. Hytrel: Polyester elastomers available from DuPont-Toray Co.,Ltd. HPF 1000: DuPont ™ HPF1000 HPF 2000: DuPont ™ HPF 2000 Himilan,AM7318, AM7327, AM7329: Ionomers available from DuPont-MitsuiPolychemicals Co., Ltd. Surlyn: An ionomer available from E.I. DuPont deNemours & Co. AN 4221C: Available under the trade name “Nucrel” fromDuPont-Mitsui Polychemicals Co., Ltd. Magnesium stearate: Available as“Magnesium Stearate G” from NOF Corporation Magnesium oxide: Availableas “Kyowamag MF-150” from Kyowa Chemical Industry Co., Ltd. Titaniumoxide: Available from Sakai Chemical Industry Co., Ltd.

Formation of Paint Film Layer (Coating Layer)

Next, the paint formulated as shown in Table 3 below was applied with anair spray gun onto the surface of the cover (outermost layer) on whichnumerous dimples had been formed, thereby producing golf balls having a15 μm-thick paint film layer formed thereon.

TABLE 3 Paint C Base resin Polyol 29.77 composition Additive 0.22 (pbw)Solvent 70.01 Curing agent Isocyanate 42 Solvent 58 Paint filmproperties Shore C hardness 62.5 Thickness (μm) 15

A polyester polyol synthesized as follows was used as the polyol in thebase resin.

A reactor equipped with a reflux condenser, a dropping funnel, a gasinlet and a thermometer was charged with 140 parts by weight oftrimethylolpropane, 95 parts by weight of ethylene glycol, 157 parts byweight of adipic acid and 58 parts by weight of1,4-cyclohexanedimethanol, following which the temperature was raised tobetween 200 and 240° C. under stirring and the reaction was effected by5 hours of heating. This yielded a polyester polyol having an acid valueof 4, a hydroxyl value of 170 and a weight-average molecular weight (Mw)of 28,000. The additives were water repellent additives. All theadditives used were commercial products. Products that weresilicone-based additives, stain resistance-improving silicone additives,or fluoropolymers having an alkyl group chain length of 7 or less wereadded.

The isocyanate used in the curing agent was Duranate™ TPA-100 (fromAsahi Kasei Corporation; NCO content, 23.1%; 100% nonvolatiles), anisocyanurate of hexamethylene diisocyanate (HMDI).

Butyl acetate was used as the base resin solvent, and ethyl acetate andbutyl acetate were used as the curing agent solvents. The Shore Chardness values in the table were obtained by preparing sheets having athickness of 2 mm, stacking together three such sheets, and carrying outmeasurement with a Shore C durometer in general accordance with ASTMD2240.

Various properties of the resulting golf balls, including the corecenter and surface hardnesses, the diameters of the core and therespective layer-encased spheres, the thickness and material hardness ofeach layer, and the surface hardness, initial velocity and compressivedeformation under specific loading of the respective layer-encasedspheres were evaluated by the following methods. The results arepresented in Table 4.

Diameters of Core, Envelope Layer-Encased Sphere and IntermediateLayer-Encased Sphere

The diameters at five random places on the surface were measured at atemperature of 23.9±1° C. and, using the average of these measurementsas the measured value for a single core, envelope layer-encased sphereor intermediate layer-encased sphere, the average diameters for ten testspecimens were determined.

Diameter of Ball

The diameters at 15 random dimple-free areas on the surface of a ballwere measured at a temperature of 23.9±1° C. and, using the average ofthese measurements as the measured value for a single ball, the averagediameter for ten measured balls was determined.

Compressive Deformations of Core, Envelope Layer-Encased Sphere,Intermediate Layer-Encased Sphere and Ball

A core, envelope layer-encased sphere, intermediate layer-encased sphereor ball was placed on a hard plate and the compressive deformation Awhen subjected to a final load of 5 kgf from an initial load of 0.2 kg,the compressive deformation B when subjected to a final load of 30 kgffrom an initial load of 5 kg, the compressive deformation C whensubjected to a final load of 60 kgf from an initial load of 5 kg and thecompressive deformation D when subjected to a final load of 130 kgf froman initial load of 10 kg were each measured. These compressivedeformations refer in each case to a measured value obtained afterholding the test specimen isothermally at 23.9° C. The instrument usedwas a high-load compression tester available from MU Instruments TradingCorporation. Measurement was carried out with the pressing head movingdownward at a speed of 4.7 mm/sec.

Core Hardness Profile

The indenter of a durometer was set substantially perpendicular to thespherical surface of the core, and the surface hardness of the core onthe Shore C hardness scale was measured in accordance with ASTM D2240.The hardness at the center of the core was measured by perpendicularlypressing the indenter of a durometer against the center region of theflat cross-section obtained by cutting the core into hemispheres. Themeasurement results are indicated as Shore C hardness values.

Material Hardnesses (Shore D Hardnesses) of Envelope Layer, IntermediateLayer and Cover

The resin materials for each of these layers were molded into sheetshaving a thickness of 2 mm and left to stand for at least two weeks,following which the Shore D hardnesses were measured in accordance withASTM D2240.

Surface Hardnesses (Shore D Hardnesses) of Envelope Layer-EncasedSphere, Intermediate Layer-Encased Sphere and Ball

Measurements were taken by pressing the durometer indenterperpendicularly against the surface of each sphere. The surface hardnessof the ball (cover) is the measured value obtained at dimple-free places(lands) on the ball surface. The Shore D hardnesses were measured with atype D durometer in accordance with ASTM D2240.

Initial Velocities of Core, Envelope Layer-Encased Sphere, IntermediateLayer-Encased Sphere and Ball

The initial velocity was measured using an initial velocity measuringapparatus of the same type as the USGA drum rotation-type initialvelocity instrument approved by the R&A. The cores, envelopelayer-encased spheres, intermediate layer-encased spheres and balls(referred to collectively below as the “test spheres”) were tested in achamber at a room temperature of 23.9±2° C. after being heldisothermally in a 23.9±1° C. environment for at least 3 hours. Each testsphere was hit using a 250-pound (113.4 kg) head (striking mass) at animpact velocity of 143.8 ft/s (43.83 m/s). One dozen test spheres wereeach hit four times. The time taken for the test sphere to traverse adistance of 6.28 ft (1.91 m) was measured and used to compute theinitial velocity (m/s). This cycle was carried out over a period ofabout 15 minutes.

TABLE 4 Example Comparative Example 1 2 3 4 1 2 3 4 5 Construction4-piece 4-piece 4-piece 4-piece 4-piece 4-piece 4-piece 4-piece 3-pieceCore Diameter (mm) 35.17 35.18 35.23 35.17 35.17 35.23 35.18 35.23 37.29Weight (g) 27.8 27.8 27.9 27.8 27.8 27.9 27.8 27.9 32.6 Compressivedeformation P (mm) 4.4 4.6 4.2 4.4 4.4 4.2 4.0 4.2 3.2 Initial velocity(m/s) 77.6 77.5 77.5 77.6 77.6 77.5 77.6 77.5 77.0 Core Surface hardness(Cs) Shore C 83.2 80.8 84.3 83.2 83.2 84.3 85.0 84.3 83.9 hardnessCenter hardness (Cc) 55.9 55.6 57.2 55.9 55.9 57.2 57.4 57.2 66.5profile Surface hardness − Center hardness 27.3 25.2 27.1 27.3 27.3 27.127.6 27.1 17.4 (Cs − Cc) Surface hardness (Cs) Shore D 48.2 46.4 49.148.2 48.2 49.1 49.6 49.1 48.8 Center hardness (Cc) 31.7 31.5 32.4 31.731.7 32.4 32.5 32.4 37.3 Surface hardness − Center hardness 16.5 14.916.7 16.5 16.5 16.7 17.1 16.7 11.5 (Cs − Cc) Envelope Material No. 1 No.1 No. 2 No. 2 No. 2 No. 1 No. 2 No. 2 — layer Thickness (mm) 1.24 1.241.22 1.25 1.25 1.21 1.25 1.22 — Material hardness (sheet hardness: ShoreD) 40 40 27 27 27 40 27 27 — Envelope Diameter (mm) 37.65 37.66 37.6737.67 37.67 37.65 37.68 37.67 — layer- Weight (g) 33.6 33.7 33.6 33.533.5 33.7 33.6 33.6 — encased Compressive deformation Q (mm) 4.05 4.303.90 4.12 4.12 3.86 3.68 3.90 — sphere Initial velocity (m/s) 77.0 77.076.9 77.0 77.0 77.0 76.8 76.9 — Surface hardness Shore D 46 46 41 41 4146 41 41 — Envelope layer surface hardness − Core Shore D 14 14 9 9 9 149 9 — center hardness Envelope layer surface hardness − Core Shore D −20 −8 −7 −7 −3 −9 −8 — surface hardness Difference in compressivedeformation between 0.38 0.29 0.33 0.31 0.31 0.36 0.33 0.33 — core andenvelope layer-encased sphere: P − Q (mm) Inter- Material No. 5 No. 5No. 5 No. 5 No. 6 No. 5 No. 3 No. 3 No. 4 mediate Thickness (mm) 1.311.30 1.29 1.30 1.28 1.31 1.29 1.29 1.36 layer Material hardness (sheethardness: Shore D) 57 57 57 57 52 57 47 47 51 Inter- Diameter (mm) 40.2740.27 40.26 40.28 40.24 40.28 40.26 40.26 40.00 mediate Weight (g) 39.5739.53 39.35 39.38 39.41 39.57 39.44 39.45 38.7 layer- Compressivedeformation R (mm) 3.61 3.78 3.58 3.76 3.76 3.44 3.49 3.71 3.01 encasedInitial velocity (m/s) 77.2 77.1 77.1 77.2 77.1 77.1 76.9 76.9 77.0sphere Surface hardness Shore D 63 63 63 63 60 63 53 53 58 Intermediatelayer surface hardness − Shore D 17 17 22 22 19 17 12 12 — Envelopelayer surface hardness Difference in compressive deformation betweenenvelope 0.44 0.52 0.32 0.36 0.37 0.42 0.19 0.19 — layer-encased sphereand intermediate layer-encased sphere: Q − R (mm) Initial velocity ofintermediate layer-encased sphere − 0.2 0.2 0.2 0.2 0.2 0.0 0.0 0.0 —Initial velocity of envelope layer-encased sphere (m/s) Cover MaterialNo. 7 No. 7 No. 7 No. 7 No. 7 No. 7 No. 7 No. 7 No. 8 Thickness (mm)1.23 1.22 1.23 1.22 1.25 1.22 1.23 1.23 1.34 Material hardness (sheethardness: Shore D) 62 62 62 62 62 62 62 62 64 Paint film Material PaintC Paint C Paint C Paint C Paint C Paint C Paint C Paint C Paint C layerMaterial hardness (sheet hardness) 62.5 62.5 62.5 62.5 62.5 62.5 62.562.5 62.5 Core center hardness − Material hardness of Shore C −6.6 −6.9−5.3 −6.6 −6.6 −5.3 −5.1 −5.3 4.0 paint film layer Ball Diameter (mm)42.73 42.72 42.72 42.72 42.73 42.72 42.73 42.73 42.67 Weight (g) 45.645.5 45.4 45.4 45.5 45.6 45.5 45.4 45.4 Compressive deformation (A)under 0.2 to 5 kg 0.17 0.16 0.13 0.17 0.14 0.16 0.17 0.18 0.13 loading(mm) Compressive deformation (B) under 5 to 30 kg 0.74 0.78 0.75 0.840.86 0.71 0.98 0.98 0.72 loading (mm) Compressive deformation (C) under5 to 60 kg 1.58 1.68 1.66 1.72 1.81 1.53 1.86 1.93 1.40 loading (mm)Compressive deformation (D) under 10 to 130 kg 2.98 3.12 3.01 3.10 3.242.89 3.20 3.31 2.64 loading (mm) Initial velocity (m/s) 77.2 77.1 77.177.1 77.3 77.1 77.0 77.1 77.3 Surface hardness Shore D 68 68 68 68 68 6868 68 71 Core surface hardness − Ball surface hardness Shore D −20 −22−19 −20 −20 −19 −18 −19 −22 Ball surface hardness − Intermediate layerShore D 5 5 5 5 8 5 15 15 13 surface hardness Difference in compressivedeformation between core and 1.45 1.47 1.22 1.33 1.18 1.33 0.81 0.920.56 ball: P − D (mm) Ball initial velocity − Core initial velocity(m/s) −0.5 −0.4 −0.5 −0.5 −0.4 −0.4 −0.6 −0.5 0.3 Ball initial velocity− Intermediate layer-encased sphere initial −0.1 0.0 0.0 0.0 0.1 0.1 0.20.2 0.3 velocity (m/s) Compressive deformation ratio D/C 1.89 1.86 1.811.80 1.79 1.89 1.72 1.72 1.88 Compressive deformation ratio D/B 4.034.02 4.00 3.69 3.75 4.08 3.27 3.37 3.64 Compressive deformation ratioD/A 17.5 19.8 22.8 18.7 23.5 18.5 18.4 18.8 20.9

The flight performance and feel at impact of each golf ball wereevaluated by the following methods. The results are shown in Table 6.

Flight Performance

Various clubs (W #1, UT #4, I #6) were mounted on a golf swing robot andthe distance traveled by the balls when struck under the conditionsshown in Table 5 below were measured and rated according to the criteriain the table.

TABLE 5 Sum of W#1 W#1 UT#4 I#6 4 conditions Clubused Product name PHYZPHYZ PHYZ PHYZ Conditions HS, 40 m/s HS, 35 m/s HS, 35 m/s HS, 35 m/sRating Good ≥205.0 m ≥176.0 m ≥160.0 m ≥140.0 m ≥683.0 m criteria NG≤204.9 m ≤175.9 m ≤159.9 m ≤139.9 m ≤682.9 m

Regarding the club name “PHYZ” in the above table, the PHYZ Driver (loftangle, 10.5°), PHYZ Utility U4 and PHYZ Iron I #6, all manufactured byBridgestone Sports Co., Ltd., were used.

Feel

Sensory evaluations were carried out when the balls were hit with adriver (W #1) by amateur golfers having head speeds of 30 to 40 m/s.Both the “soft feel” and “solid feel” of the balls were rated accordingto the following criteria.

(1) Rating Criteria for “Soft Feel”

Good: Twelve or more out of 20 golfers rated the ball as having a softfeel

Fair: From 7 to 11 out of 20 golfers rated the ball as having a softfeel

NG: Six or fewer out of 20 golfers rated the ball as having a soft feel

(2) Rating Criteria for “Solid Feel”

Good: Twelve or more out of 20 golfers rated the ball as having a solidfeel

Fair: From 7 to 11 out of 20 golfers rated the ball as having a solidfeel

NG: Six or fewer out of 20 golfers rated the ball as having a solid feel

TABLE 6 Example Comparative Example 1 2 3 4 1 2 3 4 5 Flight W#1 Spinrate (rpm) 2,830 2,774 2,801 2,761 2,679 2,853 2,719 2,693 2,755 HS, 40m/s Total distance (m) 206.5 205.6 205.3 206.1 205.4 205.8 206.0 205.3205.9 Rating good good good good good good good good good W#1 Spin rate(rpm) 2,968 2,891 2,996 2,906 2,870 3,031 2,853 2,824 2,946 HS, 35 m/sTotal distance (m) 176.8 177.2 176.6 177.3 175.7 177.0 177.3 177.8 175.8Rating good good good good NG good good good NG UT#4 Spin rate (rpm)4,389 4,355 4,442 4,372 4,316 4,481 4,405 4,328 4,247 Total distance (m)161.5 162.0 160.7 161.3 161.1 160.9 159.0 159.5 158.8 Rating good goodgood good good good NG NG NG I#6 Spin rate (rpm) 4,897 4,806 5,053 4,9105,009 4,925 5,262 4,999 5,535 Total distance (m) 141.1 141.4 140.4 140.5139.8 139.7 138.2 139.8 138.3 Rating good good good good NG NG NG NG NGSum of Total distance (m) 685.9 686.2 683.0 685.2 682.1 683.4 680.5682.4 678.8 4 conditions Rating good good good good NG good NG NG NGFeel Soft feel Rating good good good good good fair good good NG Solidfeel Rating good good good good fair good fair fair good

As demonstrated by the results in Table 6, the golf balls of ComparativeExamples 1 to 5 were inferior in the following respects to the golfballs according to the present invention that were obtained in theExamples.

In Comparative Example 1, the compressive deformation C when the ballwas subjected to a final load of 60 kg from an initial load state of 5kg was a value larger than 1.80 mm. As a result, the solid feel wasinferior and the distances traveled by the ball when hit with a driver(W #1) at a head speed of 35 m/s and when hit with a number six iron (I#6) were inferior.

In Comparative Example 2, the compressive deformation B when the ballwas subjected to a final load of 30 kg from an initial load state of 5kg was a value smaller than 0.72 mm and the compressive deformation Cwhen the ball was subjected to a final load of 60 kg from an initialload state of 5 kg was a value smaller than 1.55 mm. As a result, thesoft feel was inferior and the distance traveled by the ball when hitwith a number six iron (I #6) was inferior.

In Comparative Example 3, the compressive deformation B was a valuelarger than 0.90 mm and the compressive deformation C was a value largerthan 1.80. As a result, the solid feel was inferior and the distancestraveled by the ball when hit with a utility club and a number six ironwere inferior.

In Comparative Example 4, the compressive deformation B was a valuelarger than 0.90 mm and the compressive deformation C was a value largerthan 1.80. As a result, the solid feel was inferior and the distancestraveled by the ball when hit with a utility club and a number six ironwere inferior.

In Comparative Example 5, the compressive deformation C was a valuesmaller than 1.55 mm. As a result, the soft feel was inferior and thedistances traveled by the ball when hit with a W #1 (HS=35 m/s), autility club and a number six iron were inferior.

Comparative Examples 6 to 8

Using other company's products, namely the XXIO Premium (2018 model)from Sumitomo Rubber Industries, Ltd., the Titleist VG3 (2018 model)from Acushnet Company and the CHROME SOFT (2018 model) from CallawayGolf Company as, respectively, Comparative Example 6, ComparativeExample 7 and Comparative Example 8, the various compressivedeformations of the golf balls in these Comparative Examples weremeasured in the same way as in the above Examples. The flightperformance and feel of each of these golf balls were evaluated in thesame way as in the Examples. The compressive deformations and ballproperties are shown in Table 7. Comparative Example 6 was a three-piecesolid golf ball having a single-layer core, an intermediate layer and acover, Comparative Example 7 was a three-piece solid golf ball having atwo-layer core and a cover, and Comparative Example 8 was a four-piecesolid golf ball having a two-layer core, an intermediate layer and acover.

TABLE 7 Comparative Example 6 7 8 Construction 3-piece 3-piece 4-pieceCompressive Compressive deformation A under 0.23 0.22 0.23 deformations0.2 to 5 kg loading (mm) of ball Compressive deformation B under 1.080.96 0.82 5 to 30 kg loading (mm) Compressive deformation C under 5 to2.07 1.85 1.66 60 kg loading (mm) Compressive deformation D under 10 to3.55 3.28 3.05 130 kg loading (mm) Compressive deformation ratio D/C1.72 1.78 1.84 Compressive deformation ratio D/B 3.29 3.41 3.72Compressive deformation ratio D/A 15.6 15.2 13.5 Flight W#1: HS, 40 m/sSpin rate (rpm) 2,757 2,702 2,867 Total distance (m) 204.4 205.2 204.1Rating NG good NG W#1: HS, 35 m/s Spin rate (rpm) 2,872 2,905 3,005Total distance (m) 176.5 176.9 177.3 Rating good good good UT#4 Spinrate (rpm) 4,049 4,387 4,155 Total distance (m) 161.0 159.6 162.8 Ratinggood NG good I#6 Spin rate (rpm) 5,259 4,931 5,298 Total distance (m)139.7 141.8 138.8 Rating NG good NG Sum of 4 conditions Total distance(m) 681.5 683.5 683.0 Rating NG good good Feel Soft feel Rating goodgood good Solid feel Rating NG fair fair

As demonstrated by the results in Table 7, the golf balls of ComparativeExamples 6 to 8 were inferior in the following respects to the golfballs according to the present invention that were obtained in theExamples.

In Comparative Example 6, the compressive deformation A was a valuelarger than 0.21 mm, the compressive deformation B was a value largerthan 0.90 mm and the compressive deformation C was a value larger than1.80 mm. As a result, the solid feel was inferior, and the distancestraveled by the ball when hit with a W #1 (HS=40 m/s) and a number sixiron were inferior.

In Comparative Example 7, the compressive deformation A was a valuelarger than 0.21 mm, the compressive deformation B was a value largerthan 0.90 mm and the compressive deformation C was a value larger than1.80 mm. As a result, the solid feel was inferior and the distancetraveled by the ball when hit with a utility club was inferior.

In Comparative Example 8, the compressive deformation A was a valuelarger than 0.21 mm. As a result, the solid feel was inferior and thedistances traveled by the ball when hit with a W #1 (HS=40 m/s) and anumber six iron were inferior.

Japanese Patent Application No. 2018-169572 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A golf ball comprising a core and a cover, wherein the ball has anamount of compressive deformation such that the compressive deformationA when the ball is subjected to a final load of 5 kg from an initialload state of 0.2 kg is 0.21 mm or less, the compressive deformation Bwhen the ball is subjected to a final load of 30 kg from an initial loadstate of 5 kg is from 0.72 to 0.90 mm and the compressive deformation Cwhen the ball is subjected to a final load of 60 kg from an initial loadstate of 5 kg is from 1.55 to 1.80 mm.
 2. The golf ball of claim 1,wherein the compressive deformation D when the ball is subjected to afinal load of 130 kg from an initial load state of 10 kg is from 2.80 to3.40 mm.
 3. The golf ball of claim 2, wherein the ratio D/C betweencompressive deformation D and compressive deformation C is from 1.80 to1.90.
 4. The golf ball of claim 2, wherein the ratio D/B betweencompressive deformation D and compressive deformation B is from 3.65 to4.20.
 5. The golf ball of claim 2, wherein the ratio D/A betweencompressive deformation D and compressive deformation A is from 16.0 to25.0.
 6. The golf ball of claim 1, wherein the ball further comprises,between the core and the cover, at least an envelope layer and anintermediate layer, which golf ball has a construction of four or morelayers that includes a core, an envelope layer, an intermediate layerand a cover.
 7. The golf ball of claim 6 which satisfies the followingsurface hardness relationship: (1) Shore D hardness at surface ofcover>Shore D hardness at surface of intermediate layer>Shore D hardnessat surface of envelope layer>Shore D hardness at center of core.
 8. Thegolf ball of claim 1 wherein, letting Cc be the Shore C hardness at acenter of the core and Cs be the Shore C hardness at a surface of thecore, the Shore D hardness difference between the surface and center ofthe core (Cs−Cc) is 20 or more.
 9. The golf ball of claim 1, wherein thecover has a paint film layer formed on a surface thereof, which paintfilm layer has a material hardness that is higher than the core centerhardness (Cc).
 10. The golf ball of claim 6 which satisfies thefollowing initial velocity relationships (2), (3) and (4): (2) −0.8m/s≤(ball initial velocity−core initial velocity)≤0 m/s, (3) −0.4m/s≤(ball initial velocity−initial velocity of intermediatelayer-encased sphere)≤0.4 m/s, and (4) 0 m/s≤(initial velocity ofintermediate layer-encased sphere−initial velocity of envelopelayer-encased sphere)≤0.4 m/s.
 11. A golf ball comprising a core and acover, wherein the ball has an amount of compressive deformation suchthat, letting A be the compressive deformation when the ball issubjected to a final load of 5 kg from an initial load state of 0.2 kg,B be the compressive deformation when the ball is subjected to a finalload of 30 kg from an initial load state of 5 kg, C be the compressivedeformation when the ball is subjected to a final load of 60 kg from aninitial load state of 5 kg and D be the compressive deformation when theball is subjected to a final load of 130 kg from an initial load stateof 10 kg, D has a value of from 2.80 to 3.40 mm, the ratio D/C is from1.80 to 1.90, the ratio D/B is from 3.65 to 4.20 and the ratio D/A isfrom 16.0 to 25.0.